code: def test_setting_multiagent_key_in_config_should_fail(self):
      config = PPOConfig().multi_agent(
          policies={
              "pol1": (None, None, None, None),
              "pol2": (None, None, None, PPOConfig.overrides(lr=0.001)),
          }
      )
  
      def set_ma(config):
          # not ok: cannot set "multiagent" key in AlgorithmConfig anymore.
          config["multiagent"] = {"policies": {"pol1", "pol2"}}
  
      self.assertRaisesRegex(
          AttributeError,
          "Cannot set `multiagent` key in an AlgorithmConfig!",
          lambda: set_ma(config),
      )
  
file_path: ray/rllib/utils/tests/test_check_multi_agent.py
imports: import unittest
  from ray.rllib.algorithms.ppo import PPOConfig
  from ray.rllib.policy.policy import PolicySpec
label_desc: Use image node_id 5 for calling the TestCheckMultiAgent obj's underlying member method code with example usage: obj.test_setting_multiagent_key_in_config_should_fail() without return types